(1) Field of the Invention
The present invention relates to a process for the production of a high-hardness boron nitride film. More particularly, the present invention relates to a process for preparing a high-hardness boron nitride film by the vacuum deposition method and ion irradiation method (boron nitride will be referred to as "BN" hereinafter).
(2) Description of the Prior Art
BN includes crystal structures of cubic boron nitride (hereinafter referred to as "CBN"), hexagonal closest packing boron nitride (hereinafter referred to as "WBN") and hexagonal boron nitride (hereinafter referred to as "HBN"). Of these crystal structures, CBN and WBN are excellent in the heat shock resistance, heat conductivity, hardness and abrasion resistance and also in resistance to a metal of the iron group at high temperatures. Accordingly, application of CBN and WBN to various uses has attracted attention and investigations have been made concerning the production of high-hardness boron nitride composed mainly of CBN or WBN which has a high quality.
As one conventional production technique, a method exists in which synthesis of high-hardness boron nitride is carried out under such high pressure and temperature conditions as scores of thousands of atmospheres and one thousand and several hundreds of .degree.C. by using an expensive apparatus. Recently, studies have been made on a method in which a film of high-hardness boron nitride composed mainly CBN or WBN is formed on the surface of a substrate at a high efficiency by the gas phase growth process.
The film-forming techniques are roughly divided into the chemical deposition method and the physical deposition methods. In the field of the production of BN films, the physical deposition methods using ions are mainly investigated. These physical deposition methods include an ion beam deposition method in which an ionized atom is accelerated and is then decelerated and deposited on a substrate, a cluster ion plating method in which a cluster ion is accelerated and caused to impinge against a substrate and a large quantiy of atoms are deposited on the substrate at a time, and an in beam sputtering method in which an ionized and accelerated atom sputtered by a rare-gas or the like is deposited on a substrate. In this lost method, the kinetic energy of the ion is several eV to several hundreds of eV and the seed is barely implanted into the interior of the substrate, and therefore, the adhesion between the film and substrate is insufficient.
As another known method of producing high-hardness boron nitride, there exists an ion mixing method. According to this method, a certain substance is vacuum-depositioned on a substrate and the deposited film is irradiated with an ion seed such as a rare-gas with a kinetic energy of at least several hundreds of KeV. By such irradiation the atom of the vacuum-deposited substance is bounced by impingment of the ion seed and is caused to intrude into the interior of the substrate and a new film composed of components of both the substrate. Thereby the vacuum-deposited layer is formed between the substrate and the vacuum-deposited layer. Then, the remaining vacuum-deposited film is removed by chemical means to form a new film on the surface of the substrate. In this method, even if the energy of the ion seed becomes large, the ion current need not be increased, and large quantities of different atoms can be implanted in the vicinity of the surface of the substrate. However, this method is still insufficient in that it is difficult to maintain a constant mixing ratio between the implanted ions and the constituent atoms of the substrate.
As is seen from the foregoing description, even according to the above-mentioned film-forming techniques using ions, films of high-hardness boron nitride composed mainly of CBN or WBN have not been synthesized.